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Old 05-20-2016, 07:04 PM   #1
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Connect 1500W inverter to 2 batteries

We just purchased a Rockwood MiniLite 1905 last fall and are just starting our camping for the season. We will be boon docking most of the time at territorial camp grounds so we'd like a little bit of AC power for Keurig, toaster, etc. We have 2 x 12V AGM deep cycle batteries wired in parallel (I think, the dealer installed them).

My question is, as with our solar panels, do we hook up the positive of the inverter to 1 battery and the negative to the other?

We tried a 3000W inverter today and got the low power indicator by hooking it up the way the manual said, negative and positive to the same battery. I think perhaps the 3000W was trying to draw more power than the 2 batteries could supply. I don't want to take a chance wiring it wrong cause if I blow it up, I can't return it for a lower wattage one.

Any help would be greatly appreciated. Thanks!
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Old 05-20-2016, 07:29 PM   #2
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900w will pull about 70 amps for approximately 3minutes for a keruig. So depending on length of wire run, you would need to 6ga for 8ft and 4ga for over that length. And don't buy the stranded "speaker wire" they sell on Amazon- go to HD or lowes. Personally I think you don't have enough batteries but maybe someone with a better electronic mind can chime in.


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Old 05-20-2016, 08:05 PM   #3
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900w will pull about 70 amps for approximately 3minutes for a keruig. So depending on length of wire run, you would need to 6ga for 8ft and 4ga for over that length. And don't buy the stranded "speaker wire" they sell on Amazon- go to HD or lowes. Personally I think you don't have enough batteries but maybe someone with a better electronic mind can chime in.


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Thanks Hondaman174, will keep that in mind when we get the cables.
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Old 05-20-2016, 11:47 PM   #4
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How much battery capacity do you have?

Also, are you wiring your inverter into your main fuse panel? If so, make sure the fridge is on propane only and your converter/charger is also disconnected so it isn't trying to charge the batteries with inverter (battery) supplied alternating current.

I would recommend ditching 12V batteries and going with 2 decent golf cart batteries. You'll easily double your battery capacity and ability to draw larger loads.

I would not use anything thinner than 0 gauge wiring when connecting batteries together and running wire to an inverter. My personal RV system is 2/00 thicker cable for all battery and inverter wiring.
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Old 05-21-2016, 05:46 AM   #5
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We tried a 3000W inverter today...
The wattage of the inverter will eventually make a difference, but when you tried it, what was it supplying power for? Others are correct in that it can draw a lot of power, especially considering the two devices that you indicate you want to run. Keurig will take between 800 and 1500 watts and the toaster is probably about the same. Be aware that is at least 125 amps of 12 volt. Neither of those loads is small, both would probably run the chance of topping out your 3,000 watts. The Keurig, depending on the model, will draw 60 to 100 watts all the time if you are keeping the water "ready for coffee."

Modern inverters are good, but they do require a lot of 12 volt to run.
What size wire did you use to connect the inverter when you were trying it?
What loads were plugged into it?
If you are trying to power the entire TT and have a converter you need to turn it off (breaker or unplugging)
It is true that when connecting loads to 2 parallelled 12 volt batteries, the positive should go to one of them and the negative to the other, but that is how they should already be hooked up to your unit.
if you drink a lot of coffee and love your toast, 2 -12 volt batteries really will not do you well for more than very occasional usage.
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Old 05-21-2016, 06:42 AM   #6
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It really does not matter how big your inverter is; without the battery capacity to maintain voltage during its use will cause it to alarm and drop off line.

Trying to pull 100 amps of 12 volt power (1200 watts) from a single battery can instantly collapse the voltage below the low voltage cut off. With a pair you spread the load over two batteries and cut the voltage loss more than half.

Even at 50 amps per battery, the capacity loss is substantial and you will not get the power you need for the balance of your day without recharging (especially if you expect to use heat at night).
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Old 05-21-2016, 08:17 AM   #7
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Here's an option for you:

Many electrical units say on them how many watts they pull. Once you know that (or from manufacturers site may have to convert amps into watts) you know what sized inverter to get. Now, do you have room underneath your rear seat of your tow vehicle? I installed a 1000w inverter to power my 120v tire inflator as there will be times I will not be bringing a genny. That way I can plug in a extension cord and change tire inflation anywhere around TT. It pulls 6amp ac. Converts to about 700 watts. No problem. I even have a 4hp vacuum that pulls 900w. Ran two lines of 6ga (cause 4ga was too difficult to work around the interior) and only had a voltage drop of .1 volts and that was with wire from HD or Lowes. The cheap stuff from Amazon would instantly go to low voltage during testing. Connected to battery with 100amp resettable circuit breaker as those glass fuses delve loped their own problems after heavy use. Turn on the truck and there you go. Have been know to cook a crockpot meal while driving to destination.


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Old 05-21-2016, 11:38 AM   #8
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This site worth a look especially if you are not planning to or have not decided on powering your entire trailer or just running a dedicated line or two from your inverter.

For a small system that is budget minded and easy to install I like his approach to it.

There's some good information and videos to give you some ideas.

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Old 05-21-2016, 12:40 PM   #9
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Here's the answer to your problem with no math required:



Then enjoy your boon
docking with no worries of power.

Enjoy.

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Old 05-21-2016, 01:23 PM   #10
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Originally Posted by Livin the Life View Post
Here's the answer to your problem with no math required:



Then enjoy your boon
docking with no worries of power.

Enjoy.

My husband swears to this coffee pot. He won't even let me buy a bigger one.
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Old 05-21-2016, 01:24 PM   #11
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Boondocking

Quote:
Originally Posted by Livin the Life View Post
Here's the answer to your problem with no math required:



Then enjoy your boon
docking with no worries of power.

Enjoy.

. I had forgotten.

FIRE! Early mans first camping improvement. Came right after the hide tent!
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Old 05-21-2016, 01:58 PM   #12
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If you don't hook both (+) and (-) from inverter to the same battery, batteries wired in parallel, you are only drawing power from one battery.
Retired electrician.
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Old 05-21-2016, 02:12 PM   #13
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1500W inverter wiring

To answer your first question.
It does not matter if you wire your inverter positive and negative to the same battery or positive on one battery and negative on the other battery.
AS LONG AS YOU HAVE ADEQUATE SIZE WIRE BETWEEN THE 2 PARALLEL BATTERIES... You should have at least 4AWG between the two batteries, 2AWG is better.
These heavy gauge wires basically make the terminals on each battery the same electrical connection point voltage and current wise.

I have a 2000W inverter and 3 batteries, and at ~2000W load on inverter output I am drawing ~150 amps from my 3 batteries. With that load even with 3 batteries the battery voltage will drop below the minimum threshold within 5 to 10 minutes at best when the batteries were fully charged at the start and will drain the batteries very quickly. With my 200W solar panels and full sunshine, it will take at least 3 to 4 hours for solar to recover my batteries to full charge with no load on them.

My inverter is 10 feet from my batteries so I ran 2AWG wire from the batteries to the inverter. I have my 3 batteries wired to a marine battery switch so I can run with 2 batteries or one battery or all 3 batteries. I usually run with 2 batteries and leave 1 battery for backup. I only switch all 3 on when i am charging with solar during the day.

The point I am making here is that inverters are great for boon docking to have power overnight or all day for low power loads (<200-300W).
Yes.. you can use a Keurig or toaster oven or even microwave for around 5 to 10 minutes with 3 batteries and you will run your batteries down very quickly. If you have massive batteries, then you could run for maybe 15 to 20 minutes.

But it is going to be a huge load on your batteries and most likely drain them to the point that you will need 4 hours with 200W solar to recover them to full charge.

To give you a reference...
Your car draws from 200A to 400A when you are cranking the starter motor to start your engine. You know that if you crank continually for 2 to 3 minutes you have a dead battery. In your trailer at 2000W load you are drawing 150A on 2 to 3 batteries for a longer time and you will also end up with dead batteries at this loading within a very short time.

My advice is to just run your generator for that 10 to 15 minutes and save your batteries.
If it is daytime (solar is charging) and you want to run Keurig or toaster oven or microwave for <3-5 minutes you would probably be OK. But over that you are going to get the low voltage alarm on your inverter . If at night when you are not recharging with solar, you risk going the night without battery power.

Hope this helps.
More solar, more batteries, bigger wire... All that gives you more time.
But big loads are what generators are for.

Thanks
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Old 05-21-2016, 05:56 PM   #14
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Battery /inverter

Use very heavy cable from inverter to battery, and be sure to fuse or use a breaker on positive line from battery to inverter. Positive to first and negative to the second battery. When batteries are 12 V parallel
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Old 05-21-2016, 06:35 PM   #15
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When batteries are connected in parallel it makes no dif. where you hook the load as long as you use good heavy cable, ( DLO or welding cable) with proper termination.
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Old 05-21-2016, 07:34 PM   #16
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If you don't hook both (+) and (-) from inverter to the same battery, batteries wired in parallel, you are only drawing power from one battery.
Retired electrician.
You are joking, right ?
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Old 05-21-2016, 08:14 PM   #17
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I have a Magnum 2000w PSW inverter / charger. The manual is an excellent way to learn about inverting; and Magnum has a good one. Per my manual and from memory; if the total length of cable from inverter to battery is less than 5' #2/0 is required, if over 5' but less than 8' #4/0 is required. For 2800W and up inverters, #4/0 only. All battery to battery and battery to inverter and even battery to ground cables have to be of those wire sizes with battery to battery straps of matching lengths. My negative battery cable runs to a 500A/50mv shunt allowing a battery monitor, which attaches to the shunt using its kelvin lugs, to "see" what power is used or replaced by charging.
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Old 05-22-2016, 11:18 AM   #18
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We bought a 1500w modified sinewave inverter to run our Kerig in the morning. We plug our shorepower cord with the 120v connector into the inverter and turn the breaker off for the converter in the trailer. We have 2 deep cell 6v batteries. We have made up to 9 cups of coffee in the morning, draining our batteries a bit, but later charge them up with a generator. The Kerig peaks out at 1350w on the inverter. We wired the inverter to the batteries using a winch connector so we can "plug in" the inverter while camping and unplug it when we leave. Wired it using the supplied 2/0 cable, 5' long. Works great for us.
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Old 05-22-2016, 11:54 AM   #19
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You are joking, right ?
Well, he is an he isn't. Actually if you wire them both to the same battery and you have two in parallel, you will discharge the battery you are connected to and the other battery will attempt to discharge into the battery you are using as you draw it down...which with an inverter is quickly due to large discharge currents.

Not an ideal situation. You don't get one, but you don't get the entire benefit of both and the second battery will be "loafing." The best way to hook up batteries in parallel is to put the positive cable on one...and the negative cable on the other. This way they both see the same load and experience the same resistance to the load. This is not only true for inverters but for the whole DC system as well.

This is pretty standard for multiple battery hookups. Of course he would be right if the negatives and positives of the batteries were not connected together!
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Old 05-22-2016, 12:02 PM   #20
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That would make sense if the two batteries were inter-connected together with 20 feet of small cable (voltage drop).
If the connecting cable is of proper size and 1 foot long the two batteries are going to drain at the same rate no matter which way the inverter is connected.
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